Question

Assume we perform a known-plaintext attack against DES with one pair of plaintext and ciphertext. How many keys do we have to test in a worst-case scenario if we apply an exhaustive key search in a straightforward way? How many on average?

Answer 1

Answer:

$2^{55}$ keys in a worst case scenario

Explanation:

So, Average will be : $2^{56} /2$

$2^{55}$(Answer)